Apple (Malus domestica) Seeds contain cyanogenic glycosides; although the amount found in most apples won't kill a person, with enough seeds (hundreds), one could die from it.
Cherry (Prunus cerasus), as well as other species (Prunus spp) such as peach (Prunus persica), plum (Prunus domestica), almond (Prunus dulcis) and apricot (Prunus armeninaca). Leaves and seeds contain cyanogenic glycosides
Potato (Solanum tuberosum) Foliage and green-tinged tubers are toxic, containing the glycoalkaloid solanine, which develops as a result of exposure to light. Causes intense digestive disturbances, nervous symptoms.
Rhubarb (Rheum rhaponticum) Leaves, but not stems, contain oxalic acid salts, causing kidney disorders, convulsions, coma. Rarely fatal.
Tomato (Solanum lycopersicum) Foliage and vines contain alkaloid poisons which cause digestive upset and nervous excitement.
Other poisonous plants
Aconite (wolfsbane, monkshood) (Aconitum napellus) The poison is concentrated in the unripe seed pods and roots, but all parts are poisonous. Causes digestive upset, nervous excitement. The juice in plant parts is often fatal.
Autumn crocus The bulbs are poisonous and cause nausea, vomiting, diarrhea. Can be fatal.
Azalea All parts of the plant are poisonous and cause nausea, vomiting, depression, breathing difficulties, coma. Rarely fatal.
Caladium / Elephant ear All parts of the plant are poisonous. Symptoms are generally irritation, pain, and swelling of tissues. If the mouth or tongue swell, breathing may be fatally blocked.
Castor Oil Plant (Ricinus communis) Castor Oil Plant; The phytotoxin is ricin, an extremely toxic water soluble protein, which is concentrated in the seed. Also present are ricinine, an alkaloid, and an irritant oil. Causes burning in mouth and throat, convulsions, and is often fatal.
Daffodil The bulbs are poisonous and cause nausea, vomiting, and diarrhea. Can be fatal.
Daphne (Daphne sp.) The berries (either red or yellow) are poisonous, causing burns to mouth and digestive tract, followed by coma. Often fatal.
Darnel/Poison Ryegrass (Lolium temulentum) The seeds and seed heads of this common garden weed may contain the alkaloids temuline and loliine. Some experts also point to the fungus ergot or fungi of the genus endoconidium both of which grow on the seed heads of rye grasses as an additional source of toxicity.
Datura nightshade Contains the alkaloids scopolamine and atropine. Datura has been used as a hallucinogenic drug, eg by the native peoples of the Americas.
Deadly nightshade (Atropa belladonna) All parts of the plant contain the toxic alkaloidatropine. The young plants and seeds are especially poisonous, causing nausea, muscle twitches, paralysis; often fatal.
Deathcamas / black snakeroot All parts of the plant are poisonous, causing nausea, severe upset.
Delphinium Contains the alkaloid Delsoline. Young plants and seeds are poisonous, causing nausea, muscle twitches, paralysis, often fatal.
Doll's eyes Berries are highly poisonous, as well as all other parts.
Dumbcane / dieffenbachia All parts are poisonous, causing intense burning, irritation, and immobility of the tongue, mouth, and throat. Swelling can be severe enough to block breathing leading to death.
Elderberry The roots are poisonous and cause nausea and digestive upset.
European Holly (Ilex aquifolium) The berries are poisonous, causing gastroenteritis.
Foxglove (Digitalis purpurea) The leaves, seeds, and flowers are poisonous, containing cardiac or other steroid glycosides. These cause irregular heartbeat, and generally digestive upset and confusion. Can be fatal.
Gifblaar (Dichapatelum cymosum ) . Well known as a livestock poison in South Africa; this plant contains the metabolic poison fluoroacetic acid.
Hemlock (Conium maculatum) All parts of the plant contain the relatively simple alkaloidconiine which causes stomach pains, vomiting, progressive paralysis of the central nervous system. Can be fatal; it is the poison which killed Socrates.
Jerusalem cherry All parts, especially the berries, are poisonous, causing nausea and vomiting. It is occasionally fatal, especially to children.
Jimson weed / datura / thorn apple / stinkweed / Jamestown weed (Datura stramonium) All parts of the plant are poisonous, causing abnormal thirst, vision distortions, delirium, incoherence, coma. Often fatal.
Laburnum All parts, especially the seeds, are poisonous, causing excitement, staggering, convulsions, coma, occasionally fatal.
Larkspur (both Delphinium and Consolida spp) Young plants and seeds are poisonous, causing nausea, muscle twitches, paralysis. Often fatal.
Manchineel (Hippomane mancinella) . All parts of this tree including the fruit contain toxic phorbol esters typical of the Euphorbiaceae.
Mayapple (Podophyllum peltatum) Green portions of the plant, unripe fruit, and especially the rhizome contain the non-alkaloid toxin podophyllotoxin which causes diarrhea, severe digestive upset.
Monkshood All parts of the plant are highly poisonous. Ancient warriors used it to poison their enemies water supplies. Used in the past for killing wolves.
Moonseed The fruits and seeds are poisonous, causing nausea and vomiting. Often fatal.
Oleander (Nerium oleander) All parts are toxic, containing nerioside, oleandroside, saponins, cardiac glycosides, but especially the leaves and woody stems. They cause severe digestive upset, heart trouble, contact dermatitis. Often fatal.
Oak most species foliage and acorns are mildly poisonous, causing digestive upset, heart trouble, contact dermatitis. Rarely fatal.
Poison-ivy (Toxicodendron radicans), Poison-oak (T. diversilobum), and Poison Sumac (T.vernix) All parts of these plants contain a highly irritating oil with urushiol (this is actually not a poison but an allergen). Skin reactions can include blisters and rashes. It spreads readily to clothes and back again, and has a very long life. Infections can follow scratching. As stated, this is an allergen, and the toxin will not effect certain people. The smoke of burning poison ivy can cause reactions in the lungs, and can be fatal.
Pokeweed (Phytolacca sp.) Leaves, berries and roots contain phytolaccatoxin and phytolaccigenin - toxin in young leaves is reduced with each boiling and draining.
Privet (Ligustrum sp.) Berries and leaves are poisonous. Berries contain ligustrin and syringin, which causes difestive disturbances, nervous symptoms. Can be fatal.
Water hemlock The root, when freshly pulled out of the ground, is extremely poisonous and contains the toxin Cicuta virosa. When dried, poison is reduced to roughly 3-5 percent of what it contained when fresh.
White snakeroot All parts are poisonous, causing nausea and vomiting. Often fatal.
Yellow jessamine All parts are poisonous, causing nausea and vomiting. Often fatal. It's possible to become ill from ingesting honey made from jessamine nectar.
Yew (Taxus baccata) All parts of the plant, except for the fleshy red bit of the fruit, contain taxane alkaloids. The seeds are especially poisonous and are quickly fatal when ingested.
Poinsettias (Euphorbia pulcherrima) Notable for not being poisonous, despite persistent beliefs to the contrary, although may cause upset stomach.